The present invention relates to semiconductor devices and methods for forming the same, and in particular, to capacitors and methods of forming the same.
Semiconductor devices typically utilize capacitors to perform various functions, such as electric charge storage, for example. A standard capacitor includes two electrodes or xe2x80x9cplatesxe2x80x9d separated from each other by a dielectric insulating material. The electrodes are typically formed of electrically conductive or semiconductive materials. The ability of a capacitor to store an electric charge depends on the capacitor area. Since many capacitors are formed above the surface of a semiconductor substrate, as the area of the capacitor increases (to increase the charge-holding capacity), the space left available on the semiconductor substrate for other devices is decreased. As a result, in order to minimize the surface area occupied by capacitors, trench capacitors have become highly favored in the semiconductor manufacturing industry.
Trench capacitors extend down from the surface of the semiconductor substrate. Thus, instead of being formed on the surface of the semiconductor substrate, the capacitor is formed in a trench which is dug in the semiconductor substrate. Accordingly, the capacitor area (and implicitly the charge-holding capacity of the capacitor) may be increased by increasing the depth and width of the trench. As will be understood, the formation of the capacitor beneath the surface of the semiconductor substrate frees up space on the surface of the semiconductor substrate for additional devices.
A recent trend in the semiconductor industry has been towards the use of silicon-on-insulator (SOI) semiconductor substrates. A standard SOI substrate includes a doped base substrate layer (typically formed of silicon), an insulator layer, and an upper doped silicon layer. SOI substrates are favored because active devices formed within an upper silicon layer are insulated from the base substrate. Therefore, device leakage through the substrate is minimized, and problems associated electrical coupling to the substrate are reduced or eliminated. The use of SOI substrates, however, presents a problem since trench openings formed in the substrate (used to form, for example, trench capacitors) must extend through the insulating layer in order for the trench capacitor to have sufficient area, thereby exposing the upper silicon layer to the base substrate layer. The problem results because the silicon base substrate layer can become electrically shorted to the upper silicon layer.
Therefore, there is currently a need for a trench capacitor which is at least partially formed in the silicon base substrate layer of an SOI substrate, and which provides electrical isolation between the silicon base substrate layer and the upper silicon layers of the SOI substrate.
The present invention is a semiconductor device including a silicon-on-insulator substrate including a base substrate, an insulator layer, and a silicon layer, and a trench capacitor including at least one trench formed in the silicon-on-insulator substrate and extending through the base substrate, the insulator layer and the silicon layer, wherein the at least one trench includes at least one insulator layer formed therein.
The above and other advantages and features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the accompanying drawings.